The main anti-war march at the Chicago Nato summit was marred by clashes between police and protesters, with several people injured and 45 arrests.

Thousands of people marched towards McCormick Place in the downtown area of the city, where 51 world leaders are meeting for the two-day summit.

However, the demonstration on Sunday ended in ugly scenes as police used batons to control the crowd. The violence came as a fifth person was charged with terrorism-related offences in in relation to alleged plots to disrupt the summit.

Sunday's demonstration was the largest anti-war protest so far, after days of marches and protests in the city centre.

Gathering at Grant Park, thousands of protesters set off south towards the site of the summit, led by around 20 Iraq veterans against the war.

Arriving two blocks west of McCormick Place, the veterans, including Scott Olsen, the protester injured in Occupy Oakland demonstrations in October, staged a symbolic "returning" of their medals, tossing them in the direction of the sprawling conference space.

That was supposed to signal the end of the march, but a group of around 30 "black bloc" activists had other ideas. The protesters, clad in black with bandanas or masks covering their faces, pushed forward through the crowd towards McCormick Place.

Chicago police, who have largely pursued a low-key strategy towards protesters, were not prepared to allow demonstrators closer to the Nato summit, and attempted to force back the crowd.

In the ensuing melee, police used baton strikes to push back protesters, with several people taken away bleeding from injuries. There was also violence towards police, with a few members of the crowd tossing plastic bottles and sticks from protest signs towards officers.

Occupy Chicago condemned the violence as "unprecedented brutality". Spokeswoman Rachael Perrotta said she had "spent the afternoon driving injured protesters from the demonstration to the Chicago action medical wellness centre".

"The back seat of my car is covered in blood," she added.

There followed a standoff between police and protesters at the intersection of Michigan Ave and Cermak, which ended more than two hours after the march's scheduled finish time of 4pm.

With protesters seemingly happy to remain in the street at the cross-section, Chicago police at one point used a long-range acoustic device (LRAD) to convey the message that protesters refusing to leave the scene could be subject to "deterrent noise".

Earlier in the day, prosecutors in Chicago charged another man with terrorism-related offences, the fifth to be charged in relation to alleged plots to disrupt the Nato summit.

In a statement, the Cook County attorney's office said Mark Nelseem, 28, has been detained over allegations of possessing explosives or incendiary devices. On Saturday, Sebastien Senakiewicz, 24, was charged with making a terrorist threat.

Three others were charged with terrorism-related offences on Friday. Brian Church, 20, from Fort Lauderdale, Florida, Jared Chase, 24, from Keene, New Hampshire, and Brent Vincent Betterly, 24, from Oakland Park, Florida – were charged with conspiracy to commit terrorism, providing material support for terrorism and possession of an explosive or incendiary device.